.f {
  width: 400px;
  height: 400px;
  background-color: pink;
}
.f:hover {
  background-color: palevioletred;
}
.f .son {
  width: 200px;
  height: 200px;
  background-color: skyblue;
}
.f .son:hover {
  background-color: greenyellow;
}
.f .son:hover .sun:nth-child(4) {
  color: lightcoral;
}
.f .son .sun {
  width: 30px;
  height: 30px;
  background-color: orange;
  color: rebeccapurple;
}
.f .son .sun:hover {
  background-color: olivedrab;
}
